The most recent version of the Groovy-Eclipse-Compiler plugin for maven is 2.6.0-01.
If necessary, 2.6.1-01-SNAPSHOT versions will be available from *http://nexus.codehaus.org/snapshots/*.

How to use the compiler plugin---Setting up the POM

In your plugin section, you must change the compiler used by the maven-compiler-plugin. Like the javac ant task, the maven-compiler-plugin does not actually compile, but rather delegates the compilation to a different artifact (in our case, the groovy-eclipse-batch artifact):

By default, this will use Groovy 1.8.4 to compile your code. If you would prefer to use 1.7.10, then add another dependency to the maven-compiler-plugin:

This will allow Groovy files to be compiled. The groovy-eclipse-compiler recognizes all settings supported by the maven-compiler-plugin.

Note that the groovy-eclipse-compiler and groovy-eclipse-batch artifacts are available in Maven-central, so there is no need to explicitly declare any extra repositories.

Setting up the source folders

There are several ways to set up your maven project to recognize Groovy source files

Do nothing

The simplest way to set up your source folders is to do nothing at all: add all of your Groovy files to src/main/java and src/test/java. This requires absolutely no extra configuration and is easy to implement. However, this is not a standard maven approach to setting up your project. If you require a more standard maven approach, then it is possible to put your Groovy files in src/main/groovy and src/test/groovy and you Java files in src/main/java and src/test/java. There are several ways of doing this.

Do almost nothing

If there is at least one file (Java or not) in src/main/java, then all files in src/main/groovy will be found. If, however, src/main/java is empty, then src/main/groovy will be ignored. You can get around this by placing an empty file in src/main/java just so that src/main/groovy will be recognized. The same is true for src/test/java and src/test/groovy. This is actually a workaround for GRECLIPSE-1221.

Use the groovy-eclipse-compiler mojo for configuring source folders

(You only need this approach if your project has an empty src/main/java or src/test/java.)

If your project has no Java files and you don't want to add an empty file in src/main/java, then you can configure source files by referencing the groovy-eclipse-compiler mojo. Just add this to the plugins section of your pom:

The <extensions>true</extensions> section is important because this redefines the default lifecycle of your project so that an extra phase is added. This phase has an extra goal attached to it that adds the two Groovy source folders.

Use the build-helper-maven-plugin

(You only need this approach if your project has an empty src/main/java or src/test/java.)

The build-helper-maven-plugin allows you to do things like adding extra source folders to your project without needing to redefine the default lifecycle. You need to add this configuration to your build plugin section:

The benefit of using this approach is that you do not need to make any changes to the default lifecycle. The downside is, of course, that you need 31 lines of configuration to do this!

Sample project and source code

There is an archetype available for this project. You can use it through a command like this:

A sample project using the compiler plugin as well as the source code for the plugin itself are available from the Codehaus.org subversion repository:

groovy-eclipse-batch-builder : a set of ant scripts and configuration files used to build the groovy-eclipse-batch artifact. This artifact is an amalgamation of all jars required for compiling Groovy and Java code in Eclipse, including ecj (the Eclipse compiler for Java), the non-UI components of Groovy-Eclipse, the Groovy jars, and various required Eclipse bundles.

org.codehaus.groovy.m2eclipse : an Eclipse plugin that provides integration between Groovy-Eclipse and m2eclipse (the Maven tooling for Eclipse).

Feature org.codehaus.groovy.m2eclipse : an Eclipse feature that is required for building and releasing the org.codehaus.groovy.m2eclipse plugin.

The sample project and archetype is not maintained as well as we would like. Some community help with this would be greatly appreciated. Please see GRECLIPSE-1285.

Why another Groovy compiler for Maven? What about GMaven?

There are several benefits that the compiler plugin provides over GMaven, but at the same time it has a few limitations. First, the benefits:

The compiler plugin does not require the creation of Java stubs so that your Groovy files can compile against Java files. This will prevent some arcane compile errors from appearing.

The Groovy-Eclipse compiler is the same inside Eclipse and inside Maven, and so configuration across the two platforms can be simplified.

The compiler plugin is a standard compiler plugin for Maven. It therefore follows all allows all the same standard configuration that the Javac compiler plugin uses. This makes it simpler to introduce Groovy into an existing Maven project. All you need to do is change the compiler plugin that the pom references.

There are some limitations:

GroovyDoc tool is not supported because the compiler plugin does not produce stubs.

Groovy Mojos are not supported.

Groovy scripts cannot be executed in your poms.

Groovy compiler options are not passed through to the compiler.

The defaultScriptExtension compiler option is not supported.

Whether or not the Groovy-Eclipse compiler plugin for Maven is appropriate for your project will depend on your requirements.

Groovy-Eclipse configurator for m2Eelipse

If you are going to be working with your maven project inside of Eclipse, it is strongly recommended that you use m2eclipse. And to use your Groovy projects with m2eclipse, you will need to install the Groovy-Eclipse configurator for m2eclipse. This feature is available any of the Groovy-Eclipse update sites (e.g., nightly, milestone, or release). Just go to your Eclipse update manager and add the Groovy-Eclipse update sites (if you haven't done so already). Select the Groovy-Eclipse M2E integration.